c - 多个结构变量无意中被分配了相同的值

Question

我的程序有一个struct，其中包含2个变量和3个函数指针，如下文件demo.h:

#ifndef DEMO_H
#define DEMO_H



typedef struct {

    int structNumber;
    char *name;

    void (* setName)(char *);

     int (* getStructNumber)();
     char *(* getName)();
} *structure;



structure newStructure(); // This function builds an object kind of, of the structure and returns a pointer to it.


#endif  

这些函数的实现在demo.c中:

#include "demo.h"
#include <stdlib.h>



structure obj; // Theres definitely something wrong with the usage of this variable in function newStructure().



void setName(char *name) {

    obj->name = name;
}



char *getName() {

    return obj->name;
}


int getStructNumber() {

    return obj->structNumber;
}



structure newStructure() {

    static int structNumber = 0;
    structNumber ++;

    structure ob = (structure)malloc(sizeof(*ob));

    // Actually I've used this obj variable
    // so that this ob is accessible in other functions too.
    // But I suppose I am not using it properly.
    // I don't wish to pass ob as a parameter to other functions.
    // The program works fine if I pass it as parameters. 
    // But I want to do it without passing it as parameters.
    obj = ob;

    ob->structNumber = structNumber;


    // Assigning the function pointers.
    ob->setName = setName;
    ob->getStructNumber = getStructNumber;
    ob->getName = getName;


    return ob;
}  

这是文件 main.c 中的 main 函数:

#include "demo.h"
#include <stdio.h>



int main() {

    void displayData(structure);

    structure str1 = newStructure();
    structure str2 = newStructure();
    structure str3 = newStructure();

    str1->setName("Robin Hood");
    str2->setName("Tiger Woods");
    str3->setName("William Shakespeare");

    displayData(str1);
    displayData(str2);
    displayData(str3);

    return 0;
}



void displayData(structure str) {

    int structNumber = str->getStructNumber();
    char *name = str->getName();

    fprintf(stdout, "Struct number = %d\n", structNumber);
    fprintf(stdout, "Name: %s\n", name);
}  

上述程序所需的输出是:

Struct number = 1
Name: Robin Hood
Struct number = 2
Name: Tiger Woods
Struct number = 3
Name: William Shakespeare 

但输出实际上是这样的:

Struct number = 3
Name: William Shakespeare
Struct number = 3
Name: William Shakespeare
Struct number = 3
Name: William Shakespeare  

所有三个结构变量都具有相同的值。
我应该如何获得所需的输出？
请帮忙!提前致谢!

Answer 1

问题在于您的 setter 和 getter 函数都对全局变量 obj 进行操作。三次调用 newstruct 后，obj 指向 str3。因此，您的所有设置和获取都只会影响 str3。解决此问题的方法是让您的 setter 和 getter 函数采用结构参数并对该参数(而不是全局参数)进行操作。